<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Promise封装AJAX操作</title>
</head>
<body>
<script>
    /**
     * 封装一个函数 sendAJAX 发送 GET AJAX 请求
     * 参数   URL
     * 返回结果 Promise 对象
     */
    function sendAJAX(url){
        return new Promise((resolve, reject) => {
            const xhr = new XMLHttpRequest();
            xhr.responseType = 'json';
            xhr.open("GET", url);
            xhr.send();
            //处理结果
            xhr.onreadystatechange = function(){
                if(xhr.readyState === 4){
                    //判断成功
                    if(xhr.status >= 200 && xhr.status < 300){
                        //成功的结果
                        resolve(xhr.response);
                    }else{
                        reject(xhr.status);
                    }
                }
            }
        });
    }

    sendAJAX('https://api.apiopen.top/getJoke')
        .then(value => {
            console.log(value);
        }, reason => {
            console.warn(reason);
        });
</script>
</body>
</html>